Must the follower (Ma'mum) perform prostration if the Imam performs it during a non-aloud prayer?
Chapter on the Description of Prayer
Al-Mughni
Book of Prayer
Primary text
If the Imam performs the prostration, the follower must follow him in prostration. This is supported by the command of the Messenger of Allah (PBUH): "The Imam is appointed only to be followed; therefore, when he prostrates, prostrate with him." Furthermore, even if the follower cannot hear the Imam (due to distance or deafness) in an aloud prayer, he would still follow the Imam's prostration, and the ruling is the same in this scenario.
Supporting text
Some scholars of our school of thought suggest that the follower has the choice between following the Imam's prostration or omitting it, although following the Imam is deemed superior.